Online Colloquium
Friday, 29 January 2021, at 01.00-02.30 p.m (UT+7)

Probing dark matter with strong gravitational lensing

Prof. Kaiki Taro Inoue

Kindai University

We invite all colloquium enthusiasts to join via the Zoom link (limited to 100 participants):
Meeting ID: 835 6679 5024
Passcode: 314068

or via Youtube live stream:

Thank you for your attention and active participation.

Colloquium coordinator,

Dr. Anton Timur Jaelani


From observations of the cosmic microwave background, large scale structures, weak lensing by clusters of galaxies, cosmologists conclude that cold dark matter is the leading candidate as the major component of matter in the universe. However, it has been known that the number of observed satellite galaxies are far smaller than the predicted number of subhalos in Milky-way sized galaxies. This discrepancy called ‘missing satellite problem’ suggests that dark matter may either not be ‘cold’ or not hosting bright dwarf galaxies in cold dark matter subhalos. In order to elucidate the nature of dark matter, I recommend to use strong gravitational lensing, which can directly map the spatial distribution of dark matter particles in the universe.  As targets, we use quasars or galaxies that are quadruply lensed by a foreground elliptical galaxy. Any dark matter halos or ‘troughs’ in sight lines would affect the flux ratios and the positions of lensed images. Enhanced by the strong lensing effects, such tiny weak lensing effects become observable using ground/space telescopes like ALMA.  With careful modeling,  we would be able to constrain the mass fluctuation of dark matter in the universe on scales of 10-1000pc, which corresponds to 106 ~ 109 solar mass scales. In this talk, I will introduce the physics of gravitational lensing, free streaming of dark matter particles , the ‘small-scale problems’ and methods for measuring dark matter (+baryon) fluctuations on scales of 10-1000pc. Then I will review our recent works and discuss future prospects.